Tuberculous Encephalitis May Be Undetectable on Magnetic Resonance Imaging but Detectable on 18F-Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography.

Neurotuberculosis (NT) continues to be a global health problem with severe morbidity and mortality. The manifestations of NT are well-known and encompass forms such as meningitis, tuberculomas, military tuberculosis, ventriculitis, and brain abscess. Data of all patients with central nervous system tuberculosis who underwent magnetic resonance imaging (MRI) and/or 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) were analyzed. Over a 7-year period (2014-2021), we encountered three patients who had dense neurological deficits and 18F-FDG PET-CT results suggesting focal cortical encephalitis. 18F-FDG PET-CT demonstrated focal hypermetabolism involving focal-regional areas of the left hemisphere that corresponded to clinical deficits in two of the three patients. Follow-up 18F-FDG PET-CT showed improvement in cortical hypermetabolism in all three patients that corresponded with clinical improvement. MRI of the brain with contrast showed subtle leptomeningeal enhancement in these areas, along with other features of NT, but it could not detect cortical involvement. A literature review also revealed some previous descriptions that seemed to be consistent with tuberculous encephalitis (TbE). TbE seems to be a distinct subset of NT and may coexist with other features of NT or disseminated tuberculosis. It may be detected by 18F-FDG PET-CT even when brain MRI does not show any evident abnormality to explain a focal neurological deficit. 18F-FDG PET-CT can be considered during the evaluation and monitoring of NT to detect TbE. The presence of TbE may affect the prognosis and treatment duration of NT.